Last week, a bunch of hackers cracked open the Siri protocol and explained how the service sends information back and forth to Apple's server. Now, another developer, known only by his twitter handle @plamoni, created a proxy server to extend the functionality of Siri on your phone.
The proxy server contains custom commands that Siri on the iPhone 4S can use. In his demo video, he shows how Siri can communicate with his indoor wireless thermostat. He is able to grab status information and turn the heat on and off.
The server works with Siri on a stock iPhone 4S handset and doesn't require any jailbreak. It only works with the iPhone 4S right now and is not ported to earlier iPhone models or the iPod touch.
He has released the proxy server to the open source community so they can experiment with it. You can grab the source code from github and check out a demo video from the developer below.